1. Field of the Invention
This invention relates to an ink composition for ink jet recording and more particularly an ink composition, comprising a water-insoluble colorant, which can provide prints having excellent water fastness.
2. Background Art
In the conventional ink jet recording system, ink droplets are ejected and deposited onto a recording paper by means of an electrostatic suction method, a pneumatic ink feed method, a method utilizing electric deformation of an piezoelectric element, and a method utilizing pressure generated by heat foaming. In this recording system, the ink used is mainly a water-base ink composition comprising a solution of a water-soluble dye dissolved in water and, dissolved therein, a humectant such as a glycol, and a penetration agent such as an alcohol or pyrrolidone.
A print provided by the water-base ink composition using a water-soluble dye has a drawback that, upon contact with water, the dye is eluted from the printed area because of its water-soluble nature. Further, in general, since the water-soluble dye has a water-soluble group, such as a carboxylic, sulfonic, or amine group, it is said to be inferior in light fastness to water-insoluble colorants.
Various water-base ink compositions and processes for producing the same have been proposed in the art in order to solve these problems. For example, Japanese Patent Laid-Open Nos. 59970/1982, 53372/1986, and 162773/1988 disclose an ink composition using a dye which is insoluble in water but soluble in a water-soluble organic solvent.
Further, Japanese Patent Laid-Open No. 4665/1984 proposes a water-base ink composition using a disperse dye, and Japanese Patent Laid-Open No. 147859/1981 proposes a water-base ink composition with a water-insoluble pigment dispersed therein.
These water-base ink compositions, however, have still room for improvement. In particular, a colorant substantially insoluble or sparingly soluble in water for the purpose of improving the water fastness of the print is likely to cause clogging of a nozzle in a recording head. The reason for the occurrence of this unfavorable phenomenon is considered to be reside in that it is not easy for a colorant insoluble or sparingly soluble in water to stably exist in a water-base ink composition and that the sparingly soluble colorant is precipitated at the front end of the nozzle in the recording head.